The present invention relates to a method and apparatus for accurately determining the volume mass of a payload delivered to a water-borne vessel.
Accurately determining the mass of material (i.e., a payload) delivered to and loaded on a water-borne vessel, such as, a barge, is important to prevent overloading of the vessel. Overloading a vessel may cause it to sink or bottom out in the waterway in which it is traveling, creating a dangerous situation.
Traditional methods of determining the payload, known as xe2x80x9cdrafting the vessel,xe2x80x9d involve the visual reading of draft lines painted on the side of the vessel. These measurements must be made manually by personnel on the vessel, both when it is empty and again after the vessel is loaded to determine the payload""s displacement of the vessel into the water. The measurements obtained from this method are then used in a formula to calculate the payload delivered into the vessel.
The traditional method has several limitations. First, manual measurements have limited accuracy and are not always reliable. This is due to variations in depth perception and human error. Second, because the water level fluctuates from moment to moment due to water disturbances from wave action, accurate measurements are difficult to obtain manually. Finally, because it is not possible to uniformly load a vessel, the port-starboard (list) and fore-aft (trim) planes are not level, thereby allowing for inaccurate estimation of the mass depending on the distribution of the payload in the vessel. In addition, the traditional methods may not take into account the twisting of the vessel caused by non-uniform loading. Non-uniform loading causes not only vertical (list) and horizontal (trim) perturbations but also can cause perturbations along a diagonal axis running from opposite corners of the vessel.
As a result of the aforementioned drawbacks, large and costly errors are made in the calculations of payloads based on traditional methods. Current methods have attempted to improve upon the accuracy of determining the weight of the payload. This has involved, in part, the use of sensors to measure the displacement of the vessel caused by the weight of the payload. For example, U.S. Pat. No. 5,547,327 issued to Bachalo describes an automated loading system for floating water-borne vessels. In this system the draft of the vessel is measured by means of pressure sensors located on the outside of the vessel below the level of water. The sensors then transmit pressure signals proportional to their depth in the water to a computer that performs the relevant calculations.
Although the above-described drafting method may eliminate the inaccuracies associated with human error, other aspects of the system are problematic. First, because the sensors are positioned underwater, they are susceptible to damage during transit (such as by collision with floating debris or protrusions from the bottom of the waterway). This makes it necessary for an operator to attach and detach the sensors before and after loading, possibly subjecting the operator to the dangers associated with working in the water in the vicinity of vessels. If the sensors are not removed and damage occurs, the underwater positioning would make them difficult to access for repair and subject the repairperson to the dangers associated with entering the water, especially when ice has formed over part of the water surface.
It would be desirable to provide a method and apparatus to accurately measure the payload delivered to a water-borne vessel that eliminates the hazards and inefficiency associated with attaching, detaching, or repairing underwater sensors and the inaccuracies associated with measurements made by humans. Further, it is desirable to provide for an accurate determination of the list, trim, and twist of the vessel to ensure a highly accurate determination of the payload delivered to the vessel.
In accomplishing the stated objectives of the invention, the mass of a payload introduced into a water-borne vessel is measured by means of an apparatus that compares the draft of the vessel in an unloaded or empty condition to a loaded or loading condition. The system is comprised of a plurality of sensors positioned about the perimeter of the vessel""s deck at a height above the waterline. The sensors produce signals representative of their height above the waterline. These signals are then transmitted to a processor, which calculates the volume and mass of the payload utilizing volumetric equations and the payload""s known density. In one embodiment, the sensors are coupled to radio transmitting devices that transmit the signals to the processor. In an alternative embodiment, the sensors are positioned and attached as described above such that the distance between each sensor at the port, starboard, fore, and aft positions of the deck are measured and inputted into a processor, which calculates the volume and mass of the payload as described above.
Another aspect of the invention provides a method for determining the mass of payload introduced into a water-borne vessel by comparing the draft of the vessel in a loaded or loading condition to the vessel""s draft in an un-loaded or empty condition. In accordance with the method, a plurality of sensors is positioned about the perimeter of a water-borne vessel by means that allow for convenient attachment and detachment. The draft of the vessel is generated from signals, representative of the distance from each sensor to the waterline, produced by the sensors. Finally, the signals are sent to a processor to determine the volume and mass of the payload from the draft information obtained from the sensors.